To Spray or Not To Spray Herbicide– That is the Question

Rob Garcia, Technical Support Manager,  discusses spring weed control and when to use herbicide products

We've had cold, wet weather in many parts of the country, which has caused many pre-emergent herbicide applications to be missed or postponed. Now that the warmer weather is on the horizon, customers are asking if they should make herbicide applications or skip this spring? My recommendation is to not skip these applications but potentially use a different product and possibly add in a post-emergent with the pre-emergent herbicide. For later applications, I recommend using Dimension® herbicide which has some post-emergent control. For greater control use irrigation to water in pre-emergents; this greatly increases control of the herbicide.

Crabgrass is one of the top weeds targeted by pre-emergents. People often ask questions around the look and growth of crabgrass. Below is a list of questions to help identify if the weed is indeed crabgrass & if you should treat-

-Crabgrass is a summer annual, so if you have weeds from last year they are probably not crabgrass

-Soil temperatures of approximately 60-70 degrees in the upper 2 inches of the soil is need for germination of crabgrass

-If it is crabgrass, you can still apply pre-emergent herbicides when the soil temps are in the 50’s 

Applications tend to get pushed further back each year. Homeowners want to get out and work in the yard to prepare for spring; however, we need to remember that our common pre-emergent herbicides have a rate per the amount of time control. Let me explain that last sentence – When you spray, the clock starts ticking and we can calculate the amount of control we should be getting. If a target weed germinates later in the year or needs warmer soil temperatures, then we may not have sufficient amounts of the herbicide for control. This will then necessitate the need for a second application or an application at a higher rate.  We should always remember that many herbicides have restrictions on the amount of applications, amount of active ingredient per year, and the frequency of applications. We may need to rotate products to abide by the label of a given product (Look for a follow-up post to discuss rotation of products & label directions). 

For non-selective herbicide applications, we need to remember that when we have cooler soil temperatures the translocation (the movement of solutions within the plant) of herbicides is slowed down. This causes the visual effects of the herbicide working to take longer and many times the homeowner feels that the herbicide has failed.  To evaluate the efficacy of a product, we should take into account the following external factors: weather(temperature and rainfall), is the weed that is trying to be controlled on the label of the product that is being used, do we have an issue with water quality that is effecting our performance? Glyphosate is negatively affected by the hardness of the water and many products stability are effected by the pH of the water. Alkaline water is much more harmful to products than acidic so in many cases a water conditioner is need to increase performance. If you often have alkaline water we suggest Breeze to help balance the pH and increase the effectiveness of your herbicide.

Bonus Tip: Another great tool for both pre-emergent and post-emergent applications is the use of growing degree day models to determine when you should be making applications. 

Check out our adjuvant and herbicide product selection on for all your lawn care needs.




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